Prenatal and postnatal flavor learning by human infants

Rearing with artificially scented mothers attenuates conditioned odor aversion in adulthood but not its amygdala dependency

The aim of the present study was to investigate whether neonatal odor experience associated with the mother affects food avoidance learning and basolateral amygdala (BLA) involvement in adulthood. Odorization of mother's nipples with banana or almond solutions from birth to weaning resulted in an impairment at adulthood of conditioned odor aversion (COA). These effects were specific to the early-experienced odor since no deficit was observed for COA to a novel odor (Experiment 1). In contrast, mere exposure to an odor in the home cage instead of on mother's nipples induced no deficit in COA at adulthood (Experiment 2). Finally, transitory inactivation of the BLA during COA acquisition in adult animals impaired the normal COA of naïve animals but also the attenuated COA of rats with early odor experience on the mother (Experiment 3). These results demonstrate that neonatal odor experience associated with the mother promotes the acquisition of appetitive memories which can interfere with food avoidance learning in adulthood. They also suggest that this early experience did not modify the BLA involvement in learned aversion.

Development of food variety in children

Eating a variety of foods is essential to achieve adequate coverage of macro- and micronutrient needs. We expose here how eating habits for a variety of foods develop in childhood, from early infancy on. Preferences for specific flavours might develop early, through milk-related flavour exposures. Breastfeeding favours the acquisition of a taste for a variety of foods. At introduction of solid foods, food preferences develop thanks to repeated exposures to a variety of foods. The persistence of these early influences is still unknown. During the third year of life, most children enter a neophobic phase during which previously liked foods are no longer accepted and introduction of new foods becomes difficult. However, habits of eating a variety of foods acquired before the neophobic phase track further on into childhood, adolescence and early adulthood. This underlines the importance of promoting the access to a variety of foods in early childhood. However, beyond the nutritional advantage of eating a varied diet, could this present any drawbacks? Providing a variety of foods generally stimulates food intake and thereby might favour obesity. More research is needed to understand the link between variety and obesity, which might be food-group dependant.

Prenatal imprinting of postnatal specific appetites and feeding behavior

Epigenetic influences on the fetus's genotype have been shown to occur during intrauterine life. Experimentally imposed extracellular dehydration in pregnant rats (a model for human hyponatremia caused by gravidic vomiting) brings about a dramatic enhancement of salt appetite not only in the dam, but also in offspring when they reach adulthood. This phenomenon has been verified in human newborn infants and adults whose mothers experienced nausea and/or vomiting during pregnancy. Alcohol consumption during pregnancy enhances its palatability for the offspring. Ingestion of olfactory test substances like anise or carrot by the mother during pregnancy gives rise to a preference for the same testants in the offspring. Under- or overnutrition in the pregnant mother appears to play a role in reprogramming the postnatal regulation of both feeding and fat reserves in offspring. Both maternal under- and overnutrition during pregnancy predispose the offspring to later development of obesity and type 2 diabetes mellitus. A careful examination of the systems concerned with the regulation of food intake, and the neurosubstances involved in such regulation, reveals some of the mechanisms by which maternal nutritional status can affect the offspring and their food-related behaviors.

Biobehavior of the human love of salt

We are beginning to understand why humans ingest so much salt. Here we address three issues: The first is whether our salt appetite is similar to that in animals, which we understand well. Our analysis suggests that this is doubtful, because of important differences between human and animal love of salt. The second issue then becomes how our predilection for salt is determined, for which we have a partial description, resting on development, conditioning, habit, and dietary culture. The last issue is the source of individual variation in salt avidity. We have partial answers to that too in the effects of perinatal sodium loss, sodium loss teaching us to seek salt, and gender. Other possibilities are suggested. From animal sodium appetite we humans may retain the lifelong enhancement of salt intake due to perinatal sodium loss, and a predisposition to learn the benefits of salt when in dire need. Nevertheless, human salt intake does not fit the biological model of a regulated sodium appetite. Indeed this archetypal 'wisdom of the body' fails us in all that has to do with behavioral regulation of this most basic need.

Children's hedonic responses to the odors of alcoholic beverages: a window to emotions

The present study of 145 children and their mothers aimed to determine whether children's responses to the odors of alcoholic beverages were related to their mothers' reasons for drinking. Mothers completed a series of questionnaires to describe the emotional context in which they drink and whether they use alcohol to "escape" by changing their state of mind and reducing feelings of dysphoria. Children participated in two age-appropriate tasks that focused on the most salient psychological attribute of an odor, its perceived hedonic valence. To this aim, we determined children's liking, reaction times, and identification of individual odors including beer and whiskey in Task 1, and their preference for beer relative to odors that differed in hedonic valence in Task 2. The type of task and behavioral measure revealed different aspects of children's responses, to alcohol odors. In Task 1, verbally identifying an odor was a more difficult task than deciding whether they liked the odor. Although there were few group differences in liking for individual odors, children of Escape drinkers took significantly longer to determine whether they liked the odors. In Task 2, children of Escape drinkers preferred beer less often, particularly when it was compared with less pleasant odors. They preferred coffee to beer odors and, if their mothers did not smoke cigarettes, preferred the odors of cigarette smoke and pyridine to beer. These children experienced the odor of alcohol more frequently and in the context of mood disturbed mothers who felt guilty and worried about their drinking. Whether children who associate the odor of alcohol with such emotional contexts display a trajectory toward or against using alcohol to escape remains unknown.

Differential transfer of dietary flavour compounds into human breast milk

Transfer of dietary flavour compounds into human milk is believed to constitute the infant's early flavour experiences. This study reports on the time-dependent transfer of flavour compounds from the mother's diet to her breast milk using a within-subject design. Eighteen lactating mothers completed three test days on which they provided a baseline milk sample prior to ingestion of capsules containing 100 mg d-carvone, l-menthol, 3-methylbutyl acetate and trans-anethole. Milk samples were collected 2, 4, 6 and 8 h post-ingestion and analysed by a dynamic headspace method and gas chromatography-mass spectroscopy. The recovery quantities were adjusted for variations in milk fat content. Concentration-time profiles for d-carvone and trans-anethole revealed a maximum around 2 h post-ingestion, whereas the profile for l-menthol showed a plateau pattern. The ester 3-methylbutyl acetate could not be detected in the milk, but a single determination showed traces (<0.4 ppb) in a 1 h milk collection. Flavour compounds appeared to be transmitted differentially from the mother's diet to her milk. The results imply that human milk provides a reservoir for time-dependent chemosensory experiences to the infant; however, volatiles from the diet are transferred selectively and in relatively low amounts.

Development of taste and food preferences in children

PURPOSE OF REVIEW

There are concerns about the rising incidence of obesity in children and their acceptance of healthy foods. Many factors affect children's food acceptance, the most salient are those enabling early exposure to culturally appropriate foods in the weaning or pre-weaning period. Parents, however, have always observed individual differences in children's willingness to take new foods. This review looks at studies that encompass both exposure to and genetic determinants of food acceptance.

RECENT FINDINGS

Children's willingness to take new foods and accept specific foods has strong-to-moderate heritability. This inherited willingness is moderated by cultural differences in early exposure to both the taste and texture of foods, giving rise to different patterns of food acceptance. Breast-feeding not only confers an advantage in food and taste acceptance but may also give rise to a preference for highly palatable 'junk food'. Modelling and flavour-conditioning may also contribute to food acceptance, whereas coaxing a child to eat may impact negatively on the intake of food. Children of obese mothers, however, react to prompting by overeating rather than food refusal. This may indicate another area where food acceptance is genetically determined.

SUMMARY

Health intervention programmes that aim to promote a healthy diet in children should start at the weaning and, to a lesser extent, the pre-weaning stage, and target maternal diet for optimal effectiveness.

Genetic and environmental determinants of children's food preferences

Omnivores have the advantage of a variety of food options but face a challenge in identifying foods that are safe to eat. Not surprisingly, therefore, children show a relative aversion to new foods (neophobia) and a relative preference for familiar, bland, sweet foods. While this may in the past have promoted survival, in the modern food environment it could have an adverse effect on dietary quality. This review examines the evidence for genetic and environmental factors underlying individual differences in children's food preferences and neophobia. Twin studies indicate that neophobia is a strongly heritable characteristic, while specific food preferences show some genetic influence and are also influenced by the family environment. The advantage of the malleability of human food preferences is that dislike of a food can be reduced or even reversed by a combination of modelling and taste exposure. The need for effective guidance for parents who may be seeking to improve the range or nutritional value of foods accepted by their children is highlighted.

Complementary feeding: a commentary by the ESPGHAN Committee on Nutrition

This position paper on complementary feeding summarizes evidence for health effects of complementary foods. It focuses on healthy infants in Europe. After reviewing current knowledge and practices, we have formulated these conclusions: Exclusive or full breast-feeding for about 6 months is a desirable goal. Complementary feeding (ie, solid foods and liquids other than breast milk or infant formula and follow-on formula) should not be introduced before 17 weeks and not later than 26 weeks. There is no convincing scientific evidence that avoidance or delayed introduction of potentially allergenic foods, such as fish and eggs, reduces allergies, either in infants considered at increased risk for the development of allergy or in those not considered to be at increased risk. During the complementary feeding period, >90% of the iron requirements of a breast-fed infant must be met by complementary foods, which should provide sufficient bioavailable iron. Cow's milk is a poor source of iron and should not be used as the main drink before 12 months, although small volumes may be added to complementary foods. It is prudent to avoid both early (<4 months) and late (>or=7 months) introduction of gluten, and to introduce gluten gradually while the infant is still breast-fed, inasmuch as this may reduce the risk of celiac disease, type 1 diabetes mellitus, and wheat allergy. Infants and young children receiving a vegetarian diet should receive a sufficient amount ( approximately 500 mL) of breast milk or formula and dairy products. Infants and young children should not be fed a vegan diet.

Early determinants of fruit and vegetable acceptance

OBJECTIVE

Our goal was to evaluate the effects of breastfeeding and dietary experiences on acceptance of a fruit and a green vegetable by 4- to 8-month-old infants.

METHODS

Forty-five infants, 44% of whom were breastfed, were assigned randomly to 1 of 2 treatment groups. One group was fed green beans, and the other was fed green beans and then peaches at the same time of day for 8 consecutive days. Acceptance of both foods, as determined by a variety of measures, was assessed before and after the home-exposure period.

RESULTS

During the initial exposure, infants ate more calories from peaches than from green beans. Breastfed infants showed greater liking of peaches, as did their mothers, who ate more fruits in general than did mothers who formula fed. Although formula-feeding mothers ate more green beans, there was no difference in their infants' acceptance of this vegetable. For breastfed and formula-fed infants, repeated dietary exposure to green beans, with or without peaches, resulted in greater consumption of green beans (56.8 vs 93.6 g). Only infants who experienced green beans with peaches displayed fewer facial expressions of distaste during feeding. Mothers were apparently unaware of these changes in acceptance.

CONCLUSIONS

Breastfeeding confers an advantage in initial acceptance of a food, but only if mothers eat the food regularly. Once weaned, infants who receive repeated dietary exposure to a food eat more of it and may learn to like its flavor. However, because infants innately display facial expressions of distaste in response to certain flavors, caregivers may hesitate to continue offering these foods. Mothers should be encouraged to provide their infants with repeated opportunities to taste fruits and vegetables and should focus not only on their infants' facial expressions but also on their willingness to continue feeding.

Variety is the spice of life: strategies for promoting fruit and vegetable acceptance during infancy

The present manuscript describes two experimental studies that were conducted to explore the effects of an 8-day exposure to a particular food or a variety of foods between and/or within meals on fruit and vegetable acceptance in 74 infants. Whether the dietary experience modified acceptance depended on the flavors of foods experienced, whether the experience occurred between or within meals or both, and whether the target food was a fruit or vegetable. In the first study, we found that 8 days of dietary exposure to pears or a variety of fruits between meals (not including pears) resulted in greater consumption of pears by the infants but this increased acceptance did not generalize to green beans. In the second study, we found that 8 days of vegetable variety both between and within meals led to increased acceptance of green beans, carrots and spinach. Those infants who experienced green beans alone or a variety of vegetables between meals also tended to eat more green beans after the exposure. These findings suggest that not only can infants clearly discriminate flavors but repeated opportunities to taste a particular or a variety of foods may promote willingness to eat fruits and vegetables, the consumption of which is generally low in the pediatric population and the acceptance of which is difficult to enhance beyond toddlerhood.

Breast milk odor via olfactometer for tube-fed, premature infants

Human newborns use odor cues to orient to their source of nutrition. However, tube-fed, premature infants have restricted chemosensory experience. New methods of introducing breast milk odor to tube-fed premature infants will permit empiric tests of the effect of controlled exposure to nutrient odor. We therefore developed an infant olfactometer and piloted its use in 7 tube-fed, premature infants in the neonatal intensive care unit. Since nonnutritive sucking shortens the amount of time required to wean from tube-feeding, we tested the effect of breast milk odor on nonnutritive sucking. Six out of 7 subjects responded to breast milk odor with an increase in number of sucks. Statistical analysis supported the hypothesis that breast milk odor reinforces nonnutritive sucking. These results indicate the feasibility and potential of this experimental approach, and warrant further study of the effect of controlled nutrient odor exposure on feeding behavior of premature infants.

Acceptability and safety of novel infant porridges containing lyophilized meat powder and iron-fortified wheat flour

BACKGROUND

Lyophilized meat powder with iron-fortified wheat flour can be used to produce an infant porridge with bioavailable iron, but its acceptability and safety are unknown.

OBJECTIVE

To evaluate the acceptability and safety of porridges containing lyophilized meat powder and iron-fortified wheat flour.

METHODS

Peruvian mothers' input was used to develop porridges without (no meat) and with meat powder (low or high chicken liver, low or high chicken thigh). Acceptability was determined by maternal hedonic scoring, 9-day infant intake, and videotape analysis of how well infants liked each porridge. Dry and cooked porridges and meat ingredients were tested for microorganisms; meats were tested for pesticides.

RESULTS

Mothers gave higher acceptability scores to the no-meat porridge, followed in order by low and high quantities of meat powder (e.g., mean +/- SD "taste"scores were 4.5 +/- 0.9 for the no-meat, 3.7 +/- 1.1 for the low-liver, and 3.3 +/- 1.1 for the high-liver porridges, p = .0001). Infants' porridge intake did not differ: 61.4 +/- 47.1 g of no-meat, 62.1 +/- 44.9 g of low-thigh, and 67.5 +/- 42.0 g of low-liver (p = .7), as supported by the video analysis. Microbiologic safety was acceptable except for marginally acceptable molds and yeasts in dry ingredients. No pesticide residues were detected.

CONCLUSIONS

Despite mothers' clear preference for no-meat porridges, infants consumed equal amounts of porridges with and without meat. Thus, if mothers can be convinced to feed the meat-containing porridges to the infants despite their own preferences, the infants will consume these porridges. The mold and yeast content of the porridge ingredients must be reduced.

Childhood Obesity: The Infancy Connection

The prevalence of overweight has risen to 19% in children aged 6 to 11 years and 17% in adolescents aged 12 to 19 years. This paper examines gestational and infancy factors that influence the risk of overweight in childhood. Important factors to eliminate the infancy connection to childhood obesity include the following: (a) maternal lifestyle patterns, (b) infant feeding transitions, and (c) environmental factors. Prevention efforts need to focus on practice, research, and public policy.

Breastfeeding and smoking: short-term effects on infant feeding and sleep

OBJECTIVE

The present experimental study was designed to determine how breastfeeding from a mother who smokes affects infants in the short-term.

METHODS

Fifteen mother-infant dyads were tested on 2 days separated by 1 week. Mothers smoked (not in the presence of their infants) on one test day and refrained from smoking on the other. For the next 3.5 hours, infants breastfed on demand. Sleep and activity patterns were monitored by placing an actigraph on the infants' leg, and milk intake was determined by weighing the infants before and after each feeding. The nicotine content of the milk was measured to determine the dose of nicotine delivered to the infants.

RESULTS

Although there was no significant difference in breast milk intake, despite the taste changes in the milk, infants spent significantly less time sleeping during the hours immediately after their mothers smoked (53.4 minutes), compared with the session when their mothers abstained from smoking (84.5 minutes). This reduction was attributable to shortening of the longest sleep bout and reductions in the amounts of time spent in both active sleep and quiet sleep. With greater doses of nicotine delivered to the infant, less time was spent in active sleep.

CONCLUSIONS

An acute episode of smoking by lactating mothers altered infants' sleep/wake patterning. Perhaps concerns that their milk would taste like cigarettes and their infants' sleep patterning would be disrupted would motivate lactating mothers to abstain from smoking and to breastfeed longer.

The importance of exposure for healthy eating in childhood: a review

Children's food preferences are strongly associated with their consumption patterns. Identifying the factors that influence preferences is therefore crucial to the development of effective interventions to improve children's diets. Perhaps the most important determinant of a child's liking for a particular food is the extent to which it is familiar. Put simply, children like what they know and they eat what they like. From the very earliest age, children's experiences with food influence both preferences and intake, and research suggests that the earlier and broader that experience, the healthier the child's diet. Laboratory studies of children's food acceptance have indicated that repeated opportunities to taste unfamiliar foods results in increased liking and consumption. In order to investigate whether these results can be replicated in real-world situations, a series of naturalistic studies testing the efficacy of exposure-based interventions have been carried out. In a school-based study large increases in liking and intake of raw red pepper were seen in 5- to 7-year olds and two further studies, in which mothers used exposure techniques to increase children's acceptance of vegetables, achieved similar results. If future large-scale interventions prove to be successful, training could be offered to health professionals or directly to parents themselves.

Psychosocial correlates of 6-n-propylthiouracil (PROP) ratings in a birth cohort

This study investigated the relation between ratings of 6-n-propylthiouracil (PROP) and two psychosocial constructs, socioeconomic status and IQ, which are related to health outcomes. A 3.2mM solution of PROP was rated by 922 32-year-old members of a birth cohort (450 women) relative to the strongest imaginable sensation of any kind using the generalised Labelled Magnitude Scale. Women had higher PROP ratings than men. Following normalisation of PROP ratings, multiple linear regression showed that higher ratings were independently associated with lower childhood socioeconomic status, lower childhood IQ scores and ratings of an imagined stimulus made on the same scale (r(2)=0.12). Results suggest that psychosocial variables, sex and scale use, in addition to established genetic determinants, may help explain variability in ratings of supra-threshold concentrations of PROP.

The International society for developmental psychobiology 39th annual meeting symposium: Alcohol and development: beyond fetal alcohol syndrome

As has been repeatedly demonstrated, alcohol can exert deleterious morphological and physiological effects during early stages in development. The present review examines nonteratological links existing between alcohol and ontogeny. Human and animal studies are taken into consideration for the analysis of fetal, neonatal, infantile, adolescent, and adult responsiveness to the drug. Sensitivity to alcohol's chemosensory and postabsorptive properties, as well as learning and memory processes mediated by such properties, are examined from this developmental perspective. The studies under discussion indicate that, within each stage in development, we can trace alcohol-related experiences capable of determining or modulating alcohol seeking and intake patterns.

Food-related sensory experience from birth through weaning: contrasted patterns in two nearby European regions

This study describes infant feeding practices among mothers from two European regions from the perspective of early sensory experiences. Two groups of mothers, one in Dijon , France (n=139), the other in Aalen , Germany (n=157) with infants aged 4-9 months were interviewed using a structured questionnaire. Clear between- and within-group differences in weaning practices were found, particularly with respect to breastfeeding duration (Aalen>Dijon) and exposure to flavour variety early in weaning (Dijon>Aalen). By 4 months, 65% of infants in Dijon and 20% in Aalen, had received their first non-milk, solid foods. Before beginning to wean, 39% of mothers in Dijon offered their infant a variety of foods "just for a taste". This was the case for only 25% of mothers in Aalen. During the first 28 days of weaning, infants in Dijon were offered a greater number of vegetables compared to those in Aalen and more frequent changes from day-to-day. Thus, while Aalen infants were likely to be exposed for a longer period to different sensory experiences via breast milk, Dijon infants tended to be exposed to a greater flavour variety during the first weeks of weaning.

Predictors and dietary consequences of frequent intake of high-sugar, low-nutrient foods in 1-year-old children participating in the ABIS study

Foods rich in sugar have been suggested to contribute to the increasing prevalence of obesity in children. The aim of this report is to investigate the dietary pattern in 1-year-old children who frequently receive foods rich in sugar but low in nutrients and to study associated demographic and parental factors. During 1977-9, 21,700 infants were invited to participate in this prospective, population-based, longitudinal cohort study. Screening questionnaires were completed for 16,070 infants after delivery. Follow-up questionnaires from 10,762 children at 1 year of age are included in the analysis. It was found that 24% of the children received sweets/pastries more often than one or two times per week. They had a higher intake of French fries, potato crisps and cream as well as a lower intake of fruit and vegetables. A frequent intake of sugar-rich, low-nutrient foods was significantly associated with several maternal factors (high intake of sweets/pastries during pregnancy, young age, mother living alone) as well as presence of older siblings. Maternal smoking during pregnancy and maternal overweight were of borderline significance. Parental education level was inversely associated with the frequency of intake of sweets/pastries in the child. Children who frequently receive sweets/pastries also have an otherwise unfavourable dietary pattern. Several parental and demographic factors were associated with this feeding pattern, especially high intake of sweets/pastries during pregnancy. Screening of pregnant women for risk predictors like consumption of sweets/pastries, young age and smoking could be possible ways of identifying children at future risk for low dietary quality.

Perinatal size and maturation of the olfactory and vomeronasal neuroepithelia in lorisoids and lemuroids

Explanations for the chemosensory abilities of newborn mammals focus primarily on food (milk) acquisition and communication (e.g., maternal-infant bonding). However, the relative importance of the main and accessory (vomeronasal) olfactory systems is hypothesized to differ at birth between altricial and precocial mammals. Strepsirrhines (lemurs and lorises) possess main and accessory olfactory systems, and vary in life-history traits related to infant dependency and maturation. Accordingly, this study examines the size and maturational characteristics of vomeronasal (VNNE) and olfactory (OE) neuroepithelia in strepsirrhines. Serially sectioned heads of 18 infant cadavers were examined microscopically for neuroepithelial distribution. Measurements were taken on the length of the nasal fossa on one side that was occupied by VNNE and OE. The data were corrected for body size using the cranial length or body mass, and were then examined for correlation with several life-history variables, as well as activity pattern. In addition, immunohistochemistry was used to identify cells in the VNNE and OE that express olfactory marker protein (OMP), a marker of mature olfactory neurons. Relative OE extent was not significantly correlated with any of the life-history variables. Relative VNNE length was negatively correlated with relative gestation length and relative neonatal mass (P<0.05). However, when we corrected for phylogenetic relationships, we found no significant correlations between either of the neuroepithelial measurements and life-history variables. Immunohistochemical findings suggest that OE has more OMP-reactive cells than VNNE in all species. OMP-reactive cells appear to be less numerous in diurnal species compared to most nocturnal species. These results indicate that the VNNE may be relatively longer at birth in altricial species. However, it remains uncertain how phylogeny and/or ontogeny may explain these findings.

Effects of age on children's intake of large and self-selected food portions

OBJECTIVE

Whether developmental periods exist in which children become particularly sensitive to environmental influences on eating is unclear. This research evaluated the effects of age on intake of large and self-selected portions among children 2 to 9 years of age.

RESEARCH METHODS AND PROCEDURES

Seventy-five non-Hispanic white children 2 to 3, 5 to 6, and 8 to 9 years of age were seen at a dinner meal in reference, large, and self-selected portion size conditions in which the size of an entrée was age-appropriate, doubled, and determined by the child, respectively. Weighed food intake data were collected. Entrée bite size and bite frequency were assessed. Height and weight measurements were obtained.

RESULTS

The effect of age on children's intake of the large portion was not significant. Entrée consumption was 29% greater (p < 0.001) and meal energy intake was 13% greater (p < 0.01) in the large portion condition than in the reference condition. Increases in entrée consumption were attributable to increases in average bite size (p < 0.001). Neither child weight nor maternal weight predicted children's intake of large portions. Self-selection resulted in decreased entrée (p < 0.05) and meal energy (p < 0.01) only among those children who ate more when served the large portion.

DISCUSSION

The results of this research confirm that serving large entrée portions promotes increased intake at meals among 2- to 9-year-old children. These findings suggest that any age-related differences in children's response to large portions are likely to be smaller than previously suspected.

Amniotic fluid can act as an appetitive unconditioned stimulus in preweanling rats

Studies in humans and animals indicate that exposure to flavors in the amniotic fluid during the later gestational period may induce preferences for those flavors. Considering that during the last prenatal period the amniotic fluid contains substances that activate the opioid system, and that this system plays a critical role in the acquisition of olfactory preferences early in life, it has been hypothesized that the amniotic fluid may acquire appetitive unconditioned properties during this period. This has been tested in an experiment in which preweanling rats were exposed to alcohol odor (CS) paired or unpaired with the intraoral infusion of amniotic fluid (US) collected on gestational day 20. The pairing of these two stimuli induced an enhanced palatability of alcohol's flavor as well an increased intake of the drug. These results support the idea that amniotic fluid acquires appetitive unconditioned properties during the last days of gestation and suggest that associative mechanisms involving the amniotic fluid could be underlying odor and taste preferences acquired through fetal exposure.

Ratio of High-Fat Diet Intake of Pups Nursed by Dams Fed Combination Diet Was Lower Than That of Pups Nursed by Dams Fed High-Fat or Low-Fat Diet

To investigate the influence of fat-feeding dams on the food choice of their pups after weaning, each of three groups of dams was fed a low-fat diet (LHD), a high-fat diet (HFD) or a two-choice diet of LFD and HFD during pregnancy and lactation. Immediately after weaning, all pups were placed on a two-choice diet program for 5 wk. The fat energy ratio (F ratio) for dams fed the two-choice diet was 31%. Although no significant differences in body weight or calorie intake were observed between these three groups of dams, liver and perirenal fat tissue weights and plasma and liver trigluceride and total-cholesterol concentrations were lower in dams fed the two-choice diet than in dams fed LHD or HFD. Both groups of pups nursed by dams fed LFD or HFD continued to eat a large amount of HFD after weaning (F ratio was over 40%). Although within first week after weaning, no significant difference in the ratio of HFD intake was observed among the three groups of pups, the ratio for pups nursed by dams fed the two-choice diet decreased after the second week. The F ratio for pups nursed by dams fed the two-choice diet was 32%. These data lead us to conclude that if dams ate more than one diet in an adequate PFC ratio, their pups would have the ability to eat adequately after weaning.

Parental influence on eating behavior: conception to adolescence

The first years of life mark a time of rapid development and dietary change, as children transition from an exclusive milk diet to a modified adult diet. During these early years, children's learning about food and eating plays a central role in shaping subsequent food choices, diet quality, and weight status. Parents play a powerful role in children's eating behavior, providing both genes and environment for children. For example, they influence children's developing preferences and eating behaviors by making some foods available rather than others, and by acting as models of eating behavior. In addition, parents use feeding practices, which have evolved over thousands of years, to promote patterns of food intake necessary for children's growth and health. However in current eating environments, characterized by too much inexpensive palatable, energy dense food, these traditional feeding practices can promote overeating and weight gain. To meet the challenge of promoting healthy weight in children in the current eating environment, parents need guidance regarding alternatives to traditional feeding practices.

Development switch in neural circuitry underlying odor-malaise learning

Fetal and infant rats can learn to avoid odors paired with illness before development of brain areas supporting this learning in adults, suggesting an alternate learning circuit. Here we begin to document the transition from the infant to adult neural circuit underlying odor-malaise avoidance learning using LiCl (0.3 M; 1% of body weight, ip) and a 30-min peppermint-odor exposure. Conditioning groups included: Paired odor-LiCl, Paired odor-LiCl-Nursing, LiCl, and odor-saline. Results showed that Paired LiCl-odor conditioning induced a learned odor aversion in postnatal day (PN) 7, 12, and 23 pups. Odor-LiCl Paired Nursing induced a learned odor preference in PN7 and PN12 pups but blocked learning in PN23 pups. 14C 2-deoxyglucose (2-DG) autoradiography indicated enhanced olfactory bulb activity in PN7 and PN12 pups with odor preference and avoidance learning. The odor aversion in weanling aged (PN23) pups resulted in enhanced amygdala activity in Paired odor-LiCl pups, but not if they were nursing. Thus, the neural circuit supporting malaise-induced aversions changes over development, indicating that similar infant and adult-learned behaviors may have distinct neural circuits.

Increased ethanol intake after prenatal ethanol exposure: studies with animals

This review analyses the most relevant studies in which ethanol intake was measured after prenatal exposure to the drug. Despite the variety in methodology, in most such studies this prenatal experience induced a higher consumption of ethanol. Several variables that may affect the expression of this phenomenon are discussed, such as gender, age at testing, period of ethanol exposure, ethanol dose and conditions during the test. The mechanisms proposed in all these studies to explain the increased ethanol intake effect are also discussed. Some of these mechanisms are related to the teratological effects of the drug on the neurochemical systems involved in the reinforcing effects of abuse drugs, as well as on the regulatory systems of stress response. Another explanation of this phenomenon is also proposed in terms of associative learning. Specifically, the increased ethanol intake effect may be the result of a conditioned preference for ethanol acquired by the fetus when exposed to the drug during the last days of gestation.

Long-term consequences of early nutrition

Nutritional and metabolic exposure during critical periods of early human development can have a long-term programming effect on health in adulthood. This is supported by evidence from epidemiological studies, numerous animal models and clinical intervention trials. An improved understanding of the mechanisms and effects of metabolic programming has the potential to contribute significantly to the prevention of some major health risks. Obesity and the metabolic syndrome, whose prevalences increase in almost all countries of the world, may have partly developmental origins. Collaboration of clinicians, epidemiologists and basic scientists in an EU funded research project on the relationship between early nutrition and later health (The EU Early Nutrition Programming Project, www.metabolic-programming.org) should provide further insights into metabolic programming and help to transfer scientific progress into clinical practice.

Orosensory considerations

The chemical senses (taste, smell, and chemical irritation) convey information from the external to the internal environment. This information influences an organism's quality of life, safety, reproductive function, and, to the present point, nutritional status. To illustrate this role, the effects of chemosensory stimulation on food choice, gastrointestinal function, and energy balance will be briefly reviewed. Each role is achieved, in part, by the chemosensory cue initiating anticipatory responses for an impending homeostatic challenge, a meal.

Learning at the breast: Preference formation for an artificial scent and its attraction against the odor of maternal milk

Human newborns are known to display spontaneous attraction to the odor of human milk. This study aimed to assess whether the positive response to human milk odor can be explained by nursing-related learning, and whether it can be easily reassigned to a novel odor associated with nursing. Infants were exposed or not to a novel odor (camomile, Ca) during nursing, and tested on day 3-4 for their preference for camomile in comparison with either a scentless control (Exp. 1), a scented control (Exp. 2), or maternal milk (Exp. 3). Prior experience with Ca modified the newborns' responses. While the Ca odor became more attractive than a scented control in the Ca-exposed group, the Ca-non-exposed group did not differentiate either stimulus. In Exp. 3, the Ca-non-exposed group preferred the milk odor to the Ca odor, whereas the Ca-exposed group displayed on average equal attraction to both stimuli. Thus, a novel odor can be learned at the breast, and gain similar attractive power than the odor of mother's milk. In sum, reinforcements related with the early episodes of breastfeeding mediate the rapid development of novel odor preferences in human infants.

Vegetable acceptance by infants: effects of formula flavors

Individual differences in acceptance patterns are evident as early as the child's first experiences with a particular food. To test hypothesis that the flavor of formula fed to infants modifies their acceptance of some foods, we conducted a within- and between-subjects design study in which two groups of 6- to 11-month-old infants were tested on two separate days. One group was currently feeding a milk-based formula whereas the other was feeding a protein hydrolysate formula, a particularly unpleasant tasting formula to adults that contains similar flavor notes (e.g., sulfur volatiles) with Brassica vegetables such as broccoli. In counterbalanced order, acceptance of pureed broccoli/cauliflower was determined during one test session and pureed carrots on the other. Although there were no group differences in the amount of carrots consumed, hydrolysate infants consumed significantly less broccoli/cauliflower relative to carrots when compared to those who were currently fed milk based formulas (F(1,72 df)=4.43; p=0.04). The mothers of hydrolysate infants were significantly more likely to report that their infants did not enjoy feeding the broccoli/cauliflower (54.2%) when compared to mothers of infants being fed milk-based formulas (28.0%; Chi-Square (1 df)=4.79; p=0.03). Such findings are consistent with prior research that demonstrated a sensory specific satiety following repeated exposure to a particular flavor in milk. We hypothesize that when infants are experiencing a flavor in milk or formula, in the short term, the preference that develops is specific to the context it is experienced in (e.g., milk). Over the longer term, the preference may generalize to other contexts such as solid foods. Hydrolysate infants were also significantly more likely to be judged by their mothers as being more active (F(1,69 df)=3.95; p=0.05) and hesitant (F(1,69 df)=6.55; p=0.01) when compared to those infants who were feeding milk-based formulas, a finding that further supports the hypothesis that mother-child dynamics surrounding early feeding impacts upon mothers' perception of their children's temperament.